Constant current transformer



Nov. 6, 1934. A. PFEIL 1,979,763

CONSTANT-CURRENT TRANSFORMER Filed Feb. 15, 1934 2 SheetsSheet lJECOIVIIIF) Nov. 6; 1934. A. PFEIL. 1,979,769 I CONSTANT CURRENTTRANSFORMER FiledFeb. 15, 1954 2 Sheets-Sheet 2 FRI/WAR! gwumvbo r/Patented Nov. 6, 1934 UNITED STATES PATENT OFFICE CONSTANT CURRENT TRANSFORMIER Application February 15, 1934, Serial No. 711,413

' 7 Claims. (Cl. 171-119) This invention relates to improvements inelectric transformers, preferably of the constant current type adaptedfor use in connection with the illumination of neon or other gaseouslighting tubes or other installations wherever a constant current typeof transformer may be suitable.

An important object of my invention comprises providing a transformer ofimproved conw struction for use in energizing gaseous discharge tubesfor illumination, advertising, and other purposes whereby maximumbrilliancy and uniform operation of such devices is attained.

Another object of my invention is to provide a transformer in which theprimary and secondary coils may be closely coupled so as to attain thenecessary high efiiciency for building up the initial high voltage inthe secondary coil necessary for starting such gaseous discharge 26*devices. To this end it is one of the objects of my invention to providean improved arrangement by which an external magnetic shunt return path,by-passing the secondary coils, may be provided without the necessityfor interposing the members of such shunt return path between theprimary and secondary coils and internally with respect to thetransformer core in order that the transformer core may be designed asabove noted to permit close coupling of the primary and secondary coilsand to have an efficient and effective shape.

The present invention further provides a better distribution and betterbalancing of the magnetic flux density, particularly in the secondaryand a better uniformity in the secondary output.

With the foregoing and other objects in view, the invention consists ofa novel construction, combination and arrangement of parts as will behereinafter more specifically described and illustrated in theaccompanying drawings, wherein is disclosed an embodiment of theinvention, but it is to be understood that changes, variations, andmodifications may be resorted to without departing from the spirit ofthe claims hereto appended.

In the accompanying drawings forming a part of this specification, andin which like numerals are employed to designate like parts throughoutthe same:

Figure 1 is a top plan view of a transformer embodying the invention.

Fig. 2 is a side elevational view of the same.

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 1.

5 Fig. 4 is an end view of the transformer.

Fig. 5 is a modification of the invention showing the core with twolegs.

Fig. 6 is another form of the invention showing the core with threelegs.

In the drawings, especially Figs. 1, 2, 3, and 4, wherein for thepurpose of illustration is shown a preferred embodiment of my invention,7 desighates a transformer core having three legs, a center leg 9 andouter legs 8 and 10, respectively- Encircling the core cross-wise or atright angles to the plane of the longitudinal dimension thereof is amagnetic shunt path 11 including magnetic gaps 12 and 13 on oppositesides of the transformer core member 7. The primary coil 14 is mountedon the center leg 9 of the core member 7 and balanced secondary coils 15and 16 are mounted on outer legs 8 and 10, respectively, of the coremember 7. The shunt path 11 is as shown in the Figs. preferably designedto have a cross-sectional area not greater than the yoke and secondarylegs of the transformer core. In the arrangement shown an all metalmagnetic return path is provided for the magnetic flux threading theprimary coil 14 and the sec- 30 ondary coils 15 and 16, such return pathbeing in the form of core member 7.

Fig. 5 shows a modification with a single secondary coil 17 encirclingleg 18 and a primary coil 19 encircling leg 20. The two legs 18 and 3520 are connected by yoke portions 21 and 22 to form the complete core ofthe transformer. Encircling the core of the transformer is a magneticshunt 23 so positioned with respect to the transformer core as toprovide magnetic gaps 24 9i) and 25 between the shunt and thetransformer core as shown.' The magnetic shunt as shown preferablyencircles the major portion of the transformer core in the plane of thelongitudinal dimension of the core in order to eliminate effectively andefficiently stray fields from the transformer core.

In Fig. 6 is shown another form of modification with the shunt path 11completelyencircling the core 7 in a plane substantially co-incidentwith the plane of the longitudinal dimension of the transformer core,instead of cross-wise or at right angles thereto as is shown in Fig. 1.

In the use of my improved transformer the current delivered by thesecondary coils is arbitrarily limited, being controlled by a regulationof the size of the air gaps between the shunt and core. Preferably theregulation of the size of these air gaps is accomplished by theinsertion of brass shims. These shims may be of fiber,

wood or other non-magnetic material or the transformer core and magneticshunt may be positioned in a container as is usual and the containerfilled with wax which upon hardening maintains their relative positions.As an impulse of alternating current builds up in the primary coil withthe secondary coils connected to a load such as a gaseous discharge tubean induced current is at the same time built up in the secondary coils,my arrangement being very effective for building up such induced currentwith the high voltage necessary to start the operation of suchgaseousdischarge tube because of the close coupling of the secondary coils withthe primary coil. This induced current develops a counter magnetic fluxpressure resisting the flow of the magnetic flux through the coremembers 8, 9 and 10 which soon reaches such proportions as to equal thebrake-down resistance of the air gaps with respect to the flow ofmagnetic flux thereacross in the shunt return paths. As soon as the airgap resistance has been broken down, a greatly increased flow ofmagnetic flux through the shunt path takes place, serving to by-pass theprimary flux from the secondary coils, with the result that there is asharp drop in the voltage of the induced current flowing through thesecondary coils to a normal operating value. This serves also to limitthe current flowing through the secondary coils, the maximum currentpermitted to flow through these coils being that required forestablishing the leakage flow of magnetic flux through the shunt pathsand across the air gaps. As the magnetic shunt path of my inventionextends externally substantially around the core of the transformer asshown in the figures, the shunt operates eflectively to constrain themagnetic flux and .prevent stray fields which ordinarily occur causingheating of the metal container used with such transformers and furtherundesirable disturbances in the operation of electrical apparatusadjacent to the transformer such as radio receivers. The presentembodiment of my invention has been disclosed in considerable detail andin several types merely for the purpose of exemplifies.- tion since inactual practice it attains the features of advantage enumerated asdesirable in the statement of the invention and the above description.

It is to be understood that by describing in detail herein anyparticular form, structure, or arrangement, it is not intended to limitthe invention beyond the terms of the several claims or the requirementsof the prior art.

Having thus described my invention, what I claim as new is:

1. A constant current transformer comprising, a core member of magneticmaterial formed to have coil supportinglegs joined by an unbroken yoke,a primary coil on one of said legs, a sec- 1 ondary coil on another ofsaid legs, and a shunt path of magnetic the major portion of said coremember and spaced of the flux generated by therefrom to provide air gapsbetween said core member and said shunt for by-passing a portion saidprimary coil from said secondary coil.

material externally encircling with a center leg and a plurality ofouter legs, a primary coil mounted on said center leg, a secondary coilmounted on each of said outer legs, and a shunt path of magneticmaterial externally encircling said core member in a plane substantiallyco-incident with the plane of the longitudinal dimension of said coremember and spaced therefrom to provide air gaps between said core memberand said shunt for shunting a portion of the flux generated by saidprimary coil from said secondary coils.

3. A constant current transformer comprising, a core member of magneticmaterial provided with a center leg and a plurality of outer legs, aprimary coil ,mounted on said center leg, a secondary coil mounted oneach of said outer legs and a closed shunt path of magnetic materialexternally encircling said core member and spaced therefrom to provideair gaps between said core member and said shunt for shunting a portionof the flux generated by said primary coil from said secondary coils.

4. A constant current transformer comprising, a core member of magneticmaterial provided with a center leg and aplurality of outer legs, aprimary coil mounted on said center leg, a secondary coil mounted oneachof said outer legs and a closed shunt path of magnetic materialencircling said core member in a plane perpendicular to the plane of thelongitudinal dimension of said core member and spaced therefrom toprovide air gaps between said core member and said shunt for'shunting aportion of the flux'generated by said primary coil from said secondarycoils.

5. A constant current transformer comprising, a core member of magneticmaterial provided with a center leg and a plurality of outer legs, aprimary coil mounted on said center leg, a secondary coil mounted oneach of said outer legs and a closed magnetic shunt of cross-sectionalarea throughout not greater than the cross-sectional area of either ofsaid outer legs encircling said core member and spaced therefrom toprovide air gaps between said core member and said shunt for shunting aportion of the flux generated by said primary coil from said secondarycoils.

6. A constant current transformercomprising, a core of magnetic materialformed to have coil supporting legs joined by a yoke, a primary coil onone of said legs, at least one secondary coil on another of said legs,and a shunt pathof magnetic material externally substantially encirclingsaid core and spaced therefrom to provide air gaps between said core andpassing a portion of the flux generated by said primary coil.

7. A constant current transformer comprising a core of magnetic materialformed to have coil supporting legs joined by a yoke, said yoke and legshaving a definite cross-sectional area, a primary coil on one of saidlegs, at least one secondary coil on another of said legs and a shuntpath of magnetic material having a cross-sectional area not greater thanthat of said yoke 1A and legs encircling a major portion of said coreand spaced therefrom to provide air gaps between said core and saidshunt for by-passing a portion of flux generated by said p ry coil.

ARTHUR PFEIL. 1

said shunt for by- 13

